After graduating from aviation school as a lieutenant in 1970, Remek began active service for the Czechoslovakair force. From 1972 to 1976 he continued his studies at the Gagarin Air Force Academy in Monino, U.S.S.R. (now Russia). In 1976 he joined the Soviet cosmonaut unit as part of the Intercosmos program. The non-Soviet cosmonauts of Intercosmos flew alongside Soviet crews on missions intended to demonstrate unity between Warsaw Pact and other countries sympathetic to the Soviet Union. On March 2, 1978, he took off aboard Soyuz 28 as a research cosmonaut along with Soviet cosmonaut Aleksey Gubarev. The crew docked with the Salyut 6 space station, where the cosmonauts conducted scientific research and experiments. After nearly eight days in space, Remek and Gubarev returned to Earth on March 10.

Remek returned to the Czechoslovak air force, where he served as assistant to the chief of the Military Research Institute for six years. In 1985 he joined the Defense Office of Czechoslovakia, and he stayed there until 1989, when he left to work for an air and space museum in Prague. In 2004 Remek was elected to the European Parliament as a member of the Czech Communist Party delegation; he served until 2013. He then was the Czech ambassador to Russia (2014–18).